1. Field of the Invention
The present invention relates generally to a revolution-speed/temperature hybrid sensor and, more particularly to a revolution-speed/temperature hybrid sensor having a sensor unit with a five-input-three-output convertor.
2. Description of the Related Art
Conventionally, a revolution-speed sensor is known in which a Hall element, a magnetic reluctance element or a photocoupler is used for detecting a rotational speed of a rotary element in, for example, automobiles. Similarly, a temperature sensor is known in which a thermistor or a diode is used for temperature sensing.
Reference is now made to FIG. 7 hereof in which a conventional revolution-speed sensor unit and a temperature sensor are shown in block diagram.
As shown in FIG. 7, the revolution-speed sensor unit 20 is comprised of a Hall element 21, a waveform shaping circuit 22, a constant voltage circuit 23, and three terminals T.sub.01, T.sub.02, T.sub.03. The temperature sensor 24 is comprised of a temperature sensor 25 which is composed of a thermistor or a diode, and two terminals T.sub.04, T.sub.05.
The terminals T.sub.01 and T.sub.03 of the revolution speed sensor unit 20 are respectively connected to a plus and a minus terminal of a battery B. As a positive voltage V.sub.B is supplied from the battery B to the terminal T.sub.01, the constant voltage circuit 23 generates a constant voltage V.sub.C out of a constant voltage V.sub.B and supplies the resultant constant voltage V.sub.C to the Hall element 21 and the waveform shaping circuit 22.
The Hall element 21 detects a change in magnetic field arising from the rotation of the rotary element and outputs a revolution speed signal S.sub.VO to the waveform shaping circuit 22. The waveform shaping circuit 22 transforms the revolution speed signal S.sub.VO through amplitude limited amplification into a pulse waveform of predetermined amplitude and outputs the latter as a revolution speed signal S.sub.V to the terminal T.sub.02.
Generally, the Hall element 21 and waveform shaping circuit 22 comprise an integral Hall IC (integrated circuit).
A temperature sensor employing a thermistor, a diode or the like is designed to achieve temperature sensing utilizing changes in electrical characteristics caused by temperature changes and outputs a sensed temperature as a temperature signal S.sub.TO to the terminals T.sub.04, T.sub.05.
To detect a revolution speed and obtain a corresponding revolution speed signal by use of the revolution speed sensor employing the Hall element 21, at least three terminals are required. Similarly, it is necessary for the temperature sensor employing the thermistor, diode, etc. to have two terminals to generate and output a temperature signal. Thus, for outputting the respective signals, the two sensors need to have five terminals (four terminals when the ground is a common or shared terminal; three terminals when the ground is a body earth).
As explained above, five terminals are required for obtaining revolution speed and temperature signals by using the conventional revolution speed sensor employing a Hall element and temperature sensor employing a thermistor or a diode. Additionally, five harnesses (four harnesses when the ground is a common or shared terminal; three terminals when the ground is a body earth) are required for generating and transmitting the two signals. As a result, an associated coupler inevitably becomes large in size, thus rendering the relevant operations difficult to carry out smoothly and efficiently.